Improved optical catheter and method for making same

ABSTRACT

Catheter apparatus having transmitting and receiving optical fibers for photometric analysis of a fluid eliminates the need for individually calibrating each catheter within a population of catheters by making substantially uniform the center-to-center spacing between the outlet aperture of each and every transmitting fiber and the inlet aperture of each and every receiving fiber of an individual catheter for all catheters within a population of catheters; and by making the size and shape of all the outlet apertures of all transmitting fibers generally uniform and the size and shape of the inlet apertures of all receiving fibers generally uniform in each catheter and from catheter to catheter and that the orientation of all transmitting fibers relative to all receiving fibers be similar.

This is a continuation of application Ser. No. 964,612 now U.S. Pat. No.4,295,470 filed Nov. 29, 1978, which is a continuation of applicationSer. No. 733,279 filed Oct. 18, 1976 and now abandoned.

RELATED APPLICATIONS

The subject matter of this application is related to the subject matterof pending application Ser. No. 733,278 filed on Oct. 18, 1976 andentitled "Improved Catheter Oximeter Apparatus and Method" (now U.S.Pat. No. 4,114,604), and to the subject matter of pending applicationSer. No. 733,280 filed on Oct. 18, 1976 and entitled "SterilizableDisposable Optical Scattering Reference Medium" (now abandoned), thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Optical catheters for performing in-vivo spectrophotometric measurementsin the blood stream or elsewhere within living organisms are well-knownin the art. (See U.S. Pat. No. 3,847,483) These have most commonly beenused for the performance of oximetry, i.e., measuring the relativeamount of the total hemoglobin within the blood stream that is in theoxygenated form. While prior art optical catheters can be usedsuccessfully for perfoming oximetry, they have a shortcoming which is ofmajor importance to the medical practioner in the care of critically-illpatients. The catheters of the prior art require that an individualcalibration be performed for each and every individual catheter that isto be used, in order to obtain accurate oxygen saturation measurements.

To perform this calibration, commonly a sterile optical catheter isinserted through the wall of a blood vessel of interest and advanced sothat its tip is at a position within the flowing blood stream where itis desired that oxygen saturation measurements be made. The patient isfrequently given a particular gas mixture to breathe; commonly a mixtureenriched in oxygen or depleted of oxygen or two such mixturessequentially, which causes the patient's blood to attain an oxygensaturation level in the regions of interest. Then, as blood samples arewithdrawn (most commonly through an open lumen of the optical catheter)measurements are made of the relative light reflectances ortransmissions at the catheter tip for the various optical wavelengthsused by the catheter oximeter system.

The blood samples must then be taken to a separate instrument (forexample, a transmissionspectrophotometer located in a centrallaboratory) where an independent measurement of the oxygen saturation ofthe one or more blood samples is made. The results of this independentmeasurement are then returned to the catheter oximeter at the patient'sbedside, so that appropriate changes may be introduced into the catheteroximeter. These changes may include changes in bias levels and/or gainsof various amplifiers in order to correct for the deviation between theinitial oxygen saturation measurement made at the time of blood samplingand the oxygen saturation measurement independently determined by theseparate instrument.

This requirement for individual calibration of catheters has obvious andimportant deficiencies. One such deficiency is the delay between thetime of catheter placement and the time at which accurate measurementsof oxygen saturation utilizing the optical catheter can be obtained.This delay deprives the physician of important information at a timewhen such information is often of the utmost importance in caring forthe patient. For example, at the time of delivery of a newborn infantwith severe respiratory distress because of prematurity, or severe RhHemolytic Disease or with other disorders, the resuscitation of thesesick infants (who may weigh only two to three pounds) is frequently aprecarious and difficult problem. This resuscitation must be institutedimmediately upon birth and the various therapeutic manipulationscompleted within a very short time period. Unfortunately, the timerequired to perform calibration procedures on prior art opticalcatheters interferes with these catheters being used to furnish bloodoxygen measurements during the course of resuscitation to guide thephysician in the resuscitation procedure.

A second deficiency associated with calibrating the optical catheters ofthe prior art relates to the uncertainties associated with the resultantcalibration. Changes in blood oxygen level occur continuously and oftenvery rapidly, making it difficult to be certain that the blood sampleand the oximeter readings are truly correlated. Further, during theprocess of blood sampling through the catheter tip, significantvariations in flow profile of the red blood cells in the region wherethe optical measurements are being made may introduce errors into theoptical measurements. In addition, the manipulations of the blood samplerequired to perform oxygen saturation measurement with an independentinstrument can introduce errors in the calibration procedure.

It is therefore highly desirable to provide catheters which do notrequire individual calibration, so that each catheter of a wholepopulation of catheters can be used to obtain blood oxygen measurementimmediately upon introduction of the catheter into a blood vessel ofinterest.

SUMMARY OF THE INVENTION

In accordance with the present inventions, improved catheters which donot require individual calibration are made by using one or moretransmitting optical fibers and one or more receiving optical fibers,having apertures at the distal ends thereof which are disposed to beimmersed in blood under test, the apertures having centroids of crosssectional area which are equidistantly spaced between each and everytransmitting fiber and each and every receiving fiber of each individualcatheter and for all catheters within a population of catheters, and bymaking the size and shape of all the outlet apertures of alltransmitting fibers generally uniform, and the size and shape of theinlet apertures of all receiving fibers generally uniform in eachcatheter and from catheter to catheter in a population of catheters, andthat the orientation of all transmitting fibers relative to allreceiving fibers be similar.

DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are sectional views of the distal ends of cathetersaccording to the present invention in which a plurality of receivingoptical fibers (R) are disposed contiguous to the transmitting opticalfiber (T) and in which the centroid of area of each receiving opticalfiber (R) is equidistantly spaced from the centroid of area of thesingle transmitting optical fiber; and

FIG. 3 is a sectional view of the distal end of another embodiment of acatheter according to the present invention in which each of thetransmitting or receiving optical fibers is positioned remotely from asingle receiving (or transmitting, respectively) optical fiber, with thecentroid of area of each of the remotely-positioned optical fibersdisposed equidistantly from the centroid of area of the single,centrally-located optical fiber; and

FIGS. 4 and 5 are sectional views of the distal ends of still otherembodiments of catheters according to the present invention in each ofwhich the centroid of area of each of a pair of receiving optical fibers(R) is equidistantly disposed from the centroid of area of each of apair of transmitting optical fibers (T); and

FIG. 6 is a sectional view of the distal end of another embodiment of acatheter according to the present invention in which the centroid ofarea of each of a plurality of rectangular receiving optical fibers (R)is equidistantly disposed from the centroid of area of a single, squaretransmitting optical fiber (T); and

FIG. 7 is a graph showing the distribution of light flux at differentwavelengths and blood conditions as a function of distance from thecentroid of area of a round transmitting optical fiber at the distal endof the catheter;

and

FIG. 8 is a sectional view of a single embodiment of a catheteraccording to the present invention in which a pair of substantiallycylindrical optical fibers are contiguously disposed at the distal endof the catheter; and

FIG. 9 is a plan view of the optical fibers of a catheter according tothe present invention engaged with a photometric measuring device at anoptically-coupled interface.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 through 6, there is shown in each figure theend sectional view of the optical fiber position at the distal ends ofoptical catheters according to the present invention. In these figures,there is at least one optical fiber designated with a "T" to indicate afiber which transmits radiation to blood under test and the endsectional view of at least one optical fiber designated with the letter"R" to indicate a fiber which receives radiation from the blood undertest. It should be understood that, with respect to FIGS. 1 through 6,the transmitting fibers and receiving fibers may be transposed in whichcase each "R" would represent an optical fiber which transmits radiationto blood under test and each letter "T" would indicate an optical fiberwhich receives radiation from the blood under test. Where more than onewaveband of radiation is transmitted to the blood under test, there maybe a number of transmitting fibers at least equal to the number ofwavebands of radiation being transmitted to the blood under test; oralternately, and preferably, all wavebands of radiation used may betransmitted sequentially down each transmitting fiber.

Radiation that is transmitted down the transmitting fiber illuminatesthe blood, and the intensity of this radiation falls off with distancebecause of scattering and absorption. Some portion of that light whichilluminates the blood is back-scattered by the red blood cells and iscollected by receiving fibers which guide this collected light back to ameasuring instrument (not shown) where the light intensity is measuredby a photodetector element. It is the total light collected by theentire portion of each and every receiving fiber that is measured by thephotodetector. To a usable approximation, for radiation of wavelengthsin the optical portion of the electro-magnetic spectrum used, and foroptical fibers having dimensions of the order of ten thousandths of aninch, the centroids of the areas of the apertures of the transmittingand receiving fibers substantially correspond with the centroids of theilluminating and the receiving light fluxes emerge from and beingcollected by the apertures of the optical fibers. For circular fibers,as shown in FIGS. 1 through 4, the centroid of the cross-sectional areaof each fiber is the center of the circle. However, fibers havingapertures with cross-sectional shapes other than circular also havecentroids of cross-section and can be used. For example, for fiberapertures having rectangular cross-sectional shape at the distal end, asshown in FIGS. 5 and 6, the centroid of such cross-section is located atthe intersection of the diagonals through the corners thereof.Similarly, if the fiber apertures have a triangular cross-sectionalshape (not shown), the centroids of such cross-sections are located atthe intersection of the bi-sectors of the sides thereof. Of course, thefibers may have other more complex cross-sectional shapes at theirapertures, and it should be understood that such apertures also havecentroids of cross-section.

Referring now to FIG. 7, the graph portion illustrates the intensity ofreceived light as a function of distance from the centroid of atransmitting fiber for two different wavelengths and two differentconditions of oxygenation of blood under test.

Specifically, in Curve 17 the intensity (or light flux) measured at the800 nanometer waveband is substantially the same for hemoglobin andoxy-hemoglobin and decays with distance away from the centroid 10 of thetransmitting optical fiber 11. Curves 21 and 19 illustrate that theradiation intensity (or light flux) measured at the 670 nanometerwaveband falls off with distance measured from the centroid 10 of thetransmitting optical fiber 11 at a more rapid rate for reducedhemoglobin (Curve 21) than for oxyhemoglobin (Curve 19). From thesecurves it can be shown that the integral of light flux received by areceiving optical fiber 13 over the total cross-section area at a givenwavelength will be the same for all equidistantly-spaced locations fromthe transmitting optical fiber 11. These curves also illustrate that fora receiving optical fiber 13' which is placed a greater distance fromtransmitting optical fiber 11 than receiving optical fiber 13, theintegral of light flux received at a given wavelength will be less foroptical fiber 13' than for optical fiber 13. Further, the light fluxreceived by fiber 13' compared with the optical flux received by fiber13 will be relatively different for different wavelengths, therebyintroducing a wavelength-dependent aspect to the change in the opticalproperties of the catheter.

Returning now to FIG. 1, it can be seen that if light at all the opticalwavebands used for the measurement is transmitted down the singleoptical fiber 12, the received light intensities of each wavebandrelative to each other waveband will be unchanged whether one receivingfiber 14 is used, or the entire array of receiving fibers 14 through 24are used, or if some number of receivers between these two cases isselected, as long a the center-to-center spacing from the transmittingfiber to each of the receiving fibers 14 through 24 remains identical.

As a practical matter, individual fibers in a group of, say, receivingfibers may break or may have poorer or better optical transmittionproperties than the average. As long as the center-to-center spacingbetween the transmitting and receiving fibers remains constant, the lossof one of a group of such receiving fibers (unless it is the only one)and the concomitant variation in the transmitting properties of suchgroup of receiving fibers will not influence the relativelight-intensities measured at the various wavelengths.

FIG. 4 illustrates an embodiment of the invention involving multipletransmitting and multiple receiving-optical fibers. In this embodiment,as long as the center-to-center spacing between all transmitting and allreceiving-optical fibers remains constant, the relativelight-intensities measured at the various wavelengths utilized will beunchanged, despite fiber breakage and variations in fibertransmissivity.

FIGS. 2 and 3 illustrate embodiments of the invention in which thetransmitting optical fibers and the receiving optical fibers are not thesame size. However, in these embodiments, it is only necessary that allof the transmitting optical fibers be identical in size to each otherand all of the receiving optical fibers be indentical in size to eachother, and that the center-to-center spacing between each of thetransmitting optical fibers and each of the associated receiving opticalfibers remains constant.

FIGS. 5 and 6 illustrate other embodiments of the invention in which allof the fibers are not circular in shape. Rather, it is only necessasrythat the transmitting fibers be similar in size and shape, and that thereceiving fibers be similar in size and shape and that the orientationof all transmitting fibers relative to all receiving fibers be similarto maintain the advantages noted above.

FIG. 3 illustrates another embodiment of the invention in which thetransmitting and receiving fibers are not contiguous to each other.However, all of the operating advantages noted above may be retained bymaking the center-to-center spacing between each transmitting opticalfiber and each receiving optical fiber substantially the same and bymaking the sizes and shapes of the transmitting optical fiberssubstantially the same within the group thereof and by making the sizesand shapes of the receiving optical fibers substantially the same withinthe group thereof.

FIG. 8 illustrates the simplest, most economic, and most readilymanufacturable embodiment of an optical catheter according to thepresent invention. In this embodiment, a single transmitting opticalfiber 11 and a single receiving optical fiber 13 of identical size areplaced contiguous to each other. This configuration minimizes the amontof fiber material required, reduces the number of processes required tomake the fibers, simplifies the sorting required of fibers, and readilyassures the relationship between optical fibers discussed above.

Referring now to FIG. 9, the improved optical catheter 26 of the presentinvention typically operates in conjunction with a photometric measuringdevice 28 which furnishes one or more wavebands of light fortransmission down the transmitting optical fiber or fibers 30 and whichhas a photodetector means for measuring the intensity of light collectedby the receiving optical fiber or fibers 32. Thus, at the proximal end34 of the present optical catheter, the optical fibers must beconveniently coupleable to such a measuring device 28. To producereliable accurate photometric measurements, a repeatable stable opticalrelationship between the proximal end 34 of the transmitting andreceiving optical fibers 30, 32 of the catheter 28 and the correspondingoptical channels 36 and 38 of such a measuring device 28 must beattained. While both the optical channels 36, 38 of such a measuringdevice and the proximal end surfaces or apertures 34 of thecorresponding optical fibers 30, 32 of the catheter 28 are nominallyflat and perpendicular to the axis of light transmission, certainvariations in geometric normality can occur and these surfaces may beirregular and imperfect. If the coupling between the optical channels36, 38 of such a measuring device and the proximal end surfaces of theoptical fibers 30,32 is less than intimate, specular reflections willoccur wherever an air/surface interface occurs, and this introducesundesirable extraneous light-intensity variations in the signals beingmeasured by such measuring device. In addition, less than intimateoptical coupling between the optical channels of such a measuring deviceand the proximal end surfaces of the corresponding optical fibers mayproduce optical interference patterns which are wavelength dependent andwhich therefore can produce spurious changes in the relativelight-intensities measured at the various wavebands being used.

To avoid the error introduced by specular reflections and byinterference patterns at the optical coupling interface 34 between ameasuring device and the optical fibers 30,32 it is important thatintimate surface contact be attained and maintained, even during usewhere patient motion and other extraneous factors may introduceundesirable forces which tend to misalign and disengage the opticalcoupling at this interface 34. In accordance with one embodiment of thepresent invention intimate contact between optical channels 36, 38 andoptical fibers 30, 32 at interface 34 is attained and maintained byusing a material in the optical fibers 30, 32 which is softer and morecompliant than the material in the optical channels 36, 38 of themeasuring device 28 with which they engage. In addition, the housing 40for the optical fibers 30, 32 be made of a material that is softer andmore compliant than the material of the housing 42 which surrounds theoptical channels 36, 38. Further, to attain and maintain this intimateoptical contact between the proximal ends 34 of the optical fibers 30,32 and the optical channels 36, 38 of the measuring device 28, it isdesirable to employ means to apply an axially-aligned force 44 to theoptical catheter housing 40 which will establish an axial force at themating surfaces between the proximal ends 34 of the optical fibers 30,32 and the optical channels 36, 38. On suitable material to use in theoptical fibers 30, 32 for interfacing with optical channels 36, 38 madeof glass having the properties referred to above is styrene.

What is claimed is:
 1. A population of catheters suitable for use duringphotometric analysis of a fluid, each member of said population ofcatheters having a single transmitting optical fiber having proximal anddistal ends with aperture means respectively formed therein forconducting radiant energy therethrough, each member of said populationof catheters also having a single receiving optical fiber havingproximal and distal ends with aperture means respectively formed thereinfor conducting radiant energy therethrough, at least some of saidtransmitting and receiving fibers within said population of cathetersdiffering sufficiently in a cross-sectional dimension from one anothersuch that calibration of individual members of said population ofcatheters would otherwise be necessary to carry out accurate photometricanalysis of the fluid even if said transmitting and receiving opticalfibers of said members were used in parallel and tangent configurationat said distal ends, said aperture means being located at said distalends of said transmitting and receiving optical fibers in each member ofsaid population of catheters so that said fibers respectively havecentroids of area spaced from one another at a fixed distance which isidentical for all members of said population of catheters such that theneed for individual calibration of each member of said population ofcatheters is eliminated despite differences in the dimensions of saidtransmitting and receiving optical fibers.
 2. A population of cathetersas set forth in claim 1, wherein all of said aperture means in saidtransmitting and receiving optical fibers within said population ofcatheters are substantially the same size and shape.
 3. A population ofcatheters as set forth in claim 2, wherein all of said transmitting andreceiving optical fibers are substantially cylindrical at the distalends thereof.
 4. A population of catheters as set forth in claim 2,wherein all of said transmitting and receiving optical fibers aresubstantially rectangular at the distal ends thereof.
 5. A method forperforming photometric analysis of fluids by employing photometricanalysis equipment in combination with any one of a population ofcatheters, each catheter so employed including a single transmittingoptical fiber and a single receiving optical fiber having proximal anddistal ends with aperture means respectively formed therein forconducting radiant energy therethrough, each of said aperture meanshaving a centroid of area associated therewith, at least some of saidtransmitting and receiving optical fibers differing sufficiently in across-sectional dimension from one another such that individualcalibration of each catheter so employed would otherwise be necessary tocarry out accurate photometric analysis of the fluids even if saidtransmitting and receiving fibers of said ones of said population ofcatheters were used in parallel and tangent configuration at said distalends, said method comprising the steps of:selecting for use onlycatheters from a population of catheters, which population of cathetershas been established such that the distance between said centroids ofarea associated with said aperture means located at said distal ends ofsaid transmitting and receiving optical fibers of each catheter in saidpopulation of catheters is identical for all catheters in saidpopulation of catheters; and operating the photometric analysisequipment using all of the catheters so selected in order to performphotometric analysis of the fluids without individually calibrating eachcatheter so selected.
 6. A method of constructing a population ofcatheters for use in performing photometic analysis of a fluid, whichpopulation of catheters does not require individualized calibrationprior to performing the photometric analysis of the fluid, each memberof said population of catheters having a single transmitting opticalfiber for transmitting radiant energy to the fluid and a singlereceiving optical fiber for receiving radiant energy from the fluid,said single transmitting and receiving optical fibers being selectedfrom a population of optical fibers, each member of said population ofoptical fibers having a proximal end and a distal end with aperturemeans formed at said distal and for conducting radiant energytherethrough, at least some of the members of said population of opticalfibers differing sufficiently in a cross-sectional dimension from oneanother such that members of a population of catheters constructed fromsaid population of optical fibers would otherwise require individualizedcalibration even if said transmitting and receiving fibers of saidmembers were used in parallel and tangent configuration at said distalends, each said distal end having a centroid-of-area associatedtherewith, said method comprising the steps of:selecting a first opticalfiber from said population of optical fibers; selecting a second opticalfiber from said population of optical fibers for positioning in fixedrelationship to said first optical fiber to form a pair of opticalfibers which respectively serve as the single transmitting and singlereceiving optical fibers of an individual member of said population ofcatheters, said second optical fiber being selected such that thedistance between said centroid-of-area associated with said aperturemeans formed in said distal end of said first optical fiber so selectedand said centroid-of-area associated with said aperture means formed insaid distal end of said second optical fiber so selected is identicalfor each pair of said first and second optical fibers so formed; placingsaid first and second optical fibers so selected in an individualcatheter; and repeating said selecting and placing steps to establish apopulation of catheters.